Post-industrial and post-consumer waste glass that is collected with the purpose of recycling is known as “cullet” Post-industrial waste glass may include waste glass that has been produced during the manufacture of any glass-containing product Post-consumer waste glass generally may include waste glass that has been collected by municipal or commercial recycling efforts, and also may include a combination of clear and/or colored glass bottles, containers, cookware, tableware, glassware, plate glass, solar panels, decorative glass, and the like.
Cullet may include a mixture of one or more types of glass, e.g., a mixture of soda-lime glass, lead crystal glass, and/or borosilicate glass. Soda-lime glass, which includes container glass and flat glass, may have a chemical composition that includes 71-75 wt % SiO2, 12-16 wt % Na2O, and 10-15wt % CaO, including all ranges and subranges therebetween. Lead crystal glass may include 54-65 wt % SiO2, 25-30 wt % PbO, and 13-15 wt % Na2O and/or K2O, and borosilicate glass may include 70-80 wt % SiO2, 7-15 wt % B2O3, 4-8 wt % Na2O and/or K2O, and Al2O3, including all ranges and subranges between those ranges. These types of glasses also may include relatively small amounts of other materials.
During the waste glass collection process, other unwanted materials may be collected along with the glass. For example, metal closures, foil labels, and/or scrap metal may be collected along with the waste glass during the collection process, and their inclusion may result in the cullet having an unacceptable concentration of heavy metals such that the cullet is not suitable for use in the production of certain glass products, e.g., glass containers.
A general object of the present disclosure, in accordance with one aspect of the disclosure, is to provide a process for removing or reducing the concentration of heavy metals in a mass of cullet. Beneficiated glass produced by the presently disclosed process may contain an acceptably low concentration of heavy metals and thus may be incorporated into a downstream glass manufacturing operation and used to make new glass products, e.g., glass containers.
The present disclosure embodies a number of aspects that can be implemented separately from or in combination with each other.
A process for cullet beneficiation in accordance with one aspect of the disclosure includes: (a) melting a mass of cutlet having a heavy metal concentration of greater than 100 ppm to form a body of molten glass; (b) introducing a precipitate agent into the body of molten glass to form a heavy metal-containing precipitate phase and a liquid beneficiated glass phase within the body of molten glass; and then (c) separating the liquid beneficiated glass phase from the precipitate phase. The precipitate phase formed within the body of molten glass has a density greater than that of the beneficiated glass phase. After the liquid beneficiated glass phase is separated from the precipitate phase in step (c), the liquid beneficiated glass phase may have a reduced concentration of heavy metals, as compared to the concentration of heavy metals in the mass of cullet.
In accordance with another aspect of the disclosure, there is provided a process for preparing a mass of cullet for use in a downstream glass manufacturing operation. The process includes (a) melting a mass of cullet in a pre-reactor located upstream of a continuous glass melting furnace to form a body of molten glass in the pre-reactor; (b) introducing an oxide of titanium or sulfur, or a mixture thereof, into the body of molten glass to form a heavy metal-containing precipitate phase and a liquid beneficiated glass phase within the body of molten glass; (c) consolidating the precipitate phase within a bottom portion of the body of molten glass such that the liquid beneficiated glass phase is located above the precipitate phase within the pre-reactor; and then (d) separating the liquid beneficiated glass phase from the precipitate phase by drawing at least a portion of the liquid beneficiated glass phase off a top portion of the body of molten glass. The mass of cullet melted in the pre-reactor has a heavy metal concentration of greater than 100 ppm and includes at least one heavy metal selected from the group consisting of lead (Ph), cadmium (Cd), chromium (Cr), and mercury (Hg). The precipitate phase formed within the body of molten glass includes at least one compound selected from the group consisting of lead titanate (PbTiO3) and lead sulfate (PbSO4).